In order to pump a chemical liquid such as a photoresist out of a bottle and apply a predetermined volume of this liquid to individual semiconductor wafers, a pump for supplying chemical liquids such as that disclosed in Patent Document 1, for example, is currently in use. This pump is divided by a diaphragm into a pump chamber and an operating chamber (a pressurization chamber in Patent Document 1), and driving the diaphragm by supplying air to or withdrawing air from the operating chamber, via a supply/withdrawal passage connected to the operating chamber, changes the volume inside the pump chamber, thereby causing the pump chamber to suction or discharge a chemical liquid.
A pump has been available that is made thin by forming its pump chamber and operating chamber to be thin and using a diaphragm comprised of a flexible film. In such a pump, the diaphragm is secured at its periphery, and consequently, during the manufacturing of the diaphragm, the area located inside the secured periphery (partitioning area) ends up being formed curved in a slight convex shape toward either the pump or the operating chamber. As a result, the diaphragm does not have any tensile force (or has only a small amount of tensile force) in the region between the position at which the diaphragm would naturally curve toward the operating chamber and the position at which the diaphragm would naturally curve toward the pump chamber.
In a pump such as that described above, the opening of the supply/withdrawal passage in the operating chamber is normally positioned at the center of the operating chamber. Therefore, during the discharging of a chemical liquid, the operating air, supplied from the supply/withdrawal passage to the operating chamber, applies a well-balanced pressing force over the entire partitioning area of the diaphragm, causing the partitioning area to begin to slightly deform starting at its center. Initially, the entire partitioning area withstands the pressing force from the operating air and remains on the operating chamber side, but when its threshold is exceeded, the entire partitioning area deforms toward the pump chamber all at once, reaching the boundary of the region in which tensile force does not occur (the boundary on the pump chamber side).
During the discharging of a chemical liquid, when the entire partitioning area of the diaphragm all at once deforms toward the boundary of the region where tensile force does not occur (the boundary on the pump chamber side), the operating force applied to the diaphragm changes (increases) rapidly. During this phenomenon, the volume of the operating chamber increases rapidly, rapidly reducing the pressure inside the operating chamber. This causes a phenomenon in which the diaphragm is pulled back toward the operating chamber, with the result that the discharging pressure pulsates, making the discharging of the chemical liquid problematically unstable. Furthermore, since the operating force applied to the diaphragm changes (increases) rapidly, it has been difficult to precisely control the discharging pressure.
Patent document 1: Japanese patent application publication No. 2003-49778